Molecular Basis of Drosophila Homeotic Gene Regulation The long-term goal of this research is to understand the molecular mechanisms underlying stable long-term maintenance of the patterns of homeotic gene expression during Drosophila development. The Trithorax Group (trxG) and Polycomb Group (PcG) proteins are directly involved in this process and are respectively required to maintain active and inactive transcriptional states established in the early embryo. Evidence suggests that they function by promoting stable changes in local chromatin structure. This proposal is to investigate the role of a Polycomb Group complex containing the ESC, E(Z), SU(Z)12 and p55 proteins as well as complexes containing TRX. These proteins have been highly conserved in diverse phyla, suggesting that their fundamental functions are ancient and highly conserved. Understanding how they function will provide new insights into the mechanisms of transcriptional regulation as well as the mechanisms underlying development of normal body plans in animals. Genetic, molecular and biochemical approaches will be used investigate their functions. We have identified ESC/E(Z) complexes associated with the histone deacetylase RPD3, implicating histone deacetylation in the mechanism of ESC/E(Z) action. TRX and PcG proteins act through the same DNA response elements, suggesting that their antagonistic activities must be managed locally at PREs. We are investigating a new protein that may provide some insights into how this regulation occurs. We will continue to investigate a number of newly identified proteins associated with ESC/E(Z) complexes and TRX complexes that are providing new insights into how the enzymatic activities of ESC/E(Z) complexes function in the epigenetic inheritance of repressed and active chromatin states. We are determining how they function in concert with TRX and ESC/E(Z) complexes to promote maintenance of transcriptional states. Mutations in the human TRX homolog MLL are associated with acute leukemias, while several human PeG proteins are implicated in immune system dysfunction and tumorigenesis. Understanding the fundamental mechanism of action of TRX and ESC/E(Z) complexes in the context of development should also provide insights into the role of their human homologs in disease.